Engine emissions may change from one engine start to another when engine speed during engine run-up changes from start to start. If engine speed increases or decreases from an expected engine speed during engine starting, engine cylinder air-fuel mixtures may change such that engine torque and emissions change. Therefore, it may be desirable to control engine speed such that engine speed is more consistent from engine start to engine start. One way to improve engine speed control during an engine start is to provide consistent cylinder air charges between different engine starts. However, it may be difficult to provide consistent cylinder air charges between engine starts due to fixed timing constraints between crankshaft and camshaft timing.
The inventors herein have recognized the above-mentioned limitations and have developed a method for adjusting engine port throttles, comprising: positioning an air inlet throttle of an engine; adjusting a first port throttle in a first position, the first port throttle located downstream of the air inlet throttle; adjusting a second port throttle in a second position, different than the first position, the second port throttle located downstream of the air inlet throttle; and starting an engine after positioning the first and second port throttles.
By individually adjusting port throttles during engine starting, it may be possible to provide more consistent cylinder air charges between engine cylinders during engine starting. For example, different port throttles of an engine may be adjusted to different positions during an engine start so as to regulate air entering cylinders based on intake manifold pressure, port throttle position, and cylinder intake valve timing. Consequently, an amount of air entering a particular cylinder may be adjusted by changing the position of the port throttle. In this way, individual cylinder air amounts may be controlled even though intake valve timing between cylinders is substantially the same.
The present description may provide several advantages. For example, the approach may provide more precise control of engine speed, air charge, and air-fuel ratio from engine start to engine start. Further, individual control of engine cylinder port throttles may improve engine position control during engine stopping. Additionally, the approach may provide cylinder air charge control for engines having fixed valve timing that approaches that of engines having valves that are adjustable independent of crankshaft position.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.